BIM-UHF Radiometrix, BIM-UHF Datasheet - Page 7

• Manufacturer Part Number: BIM-UHF
• Description: Low Power UHF Data Transceiver Module
• Manufacturer: Radiometrix

Antenna requirements
Three types of integral antenna are recommended and approved for use with the BiM transceiver :
A) Helical:
B) Loop,
C) Whip
Radiometrix Ltd, BiM Data Sheet
figure 4: signal to noise curve
figure 5: timing waveforms
Wire coil, connected directly to pin 2, open circuit at other end. This antenna is very
efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim
the wire length or expand the coil for optimum results. The helical de-tunes badly with
proximity to other conductive objects.
A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and
fed from pin 2 at a point 20% from the ground end. Loops have high immunity to
proximity de-tuning.
This is a wire, rod ,PCB track or combination connected directly to pin 2 of the module.
Optimum total length is 17cm (1/4 wave @ 418MHz) Keep the open circuit (hot) end well
away from metal components to prevent serious de-tuning. Whips are ground plane
sensitive and will benefit from internal 1/4 wave earthed radial(s) if the product is small
and plastic cased.
page 7